Electrical components which are used to establish various circuit contacts should have a low, stable contact resistance, which can be assured only if the contact metal is a good conductor and does not substantially deteriorate with time. Noble metals, such as gold and the metals of the platinum family have very low chemical reactivity, essentially do not oxidize or form sulfides, and therefore meet the foregoing requirements. However, the cost of the noble metals adversely affect the economies of making low-energy, low-cost circuit contacts therefrom.
A noble metal may be electrodeposited on a base metal substrate to give the desired low energy contact resistance, but in any event the base metal substrate must be essentially pore free and have good conductivity to take proper advantage of the noble metal being electrodeposited thereover. For example, if a base metal is porous, deposits can cause films to be formed on the contact, which films are produced by corrosion products resulting either from the tarnishing of the base metal substrate or from a directly coupled corrosion between the base substrate and the noble metals.
Palladium, because it is a less expensive metal than gold and is a relatively unreactive member of the platinum family, can effectively replace gold for some contact applications. Palladium does wear better than gold and the density of palladium is lower than the density of gold, so that for equal thicknesses, the relative expense of the same thickness of the metal contact can be decreased through the use of palladium. Where it is essential to use an external gold layer, advantages can be obtained by applying a base layer of palladium as a portion of the total thickness of the substrate and plating gold thereover. However, the cost of palladium is still relatively significant and any ability to lower the cost of the substrate or final plated product has obvious economic advantages to the user.
While the use of palladium as a substitute metal for gold as an electrical component contact material is relatively well known, palladium alloy material is not. U.S. Pat. No. 3,925,170, issued Dec. 9, 1975, does disclose a plating bath for producing bright palladium electrodepositions which uses small amounts of cobalt or nickel as a brightener for the electrodeposit, but does not use sufficient quantities of either to substantially affect the cost of the plated contact. In one example given, the nickel added to the bath is substantially less than one quarter of the palladium ion included in the bath and since palladium plates faster than nickel, the resultant nickel in the electrodeposit would be expected to be significantly less than 5% of the total deposit.